POLARON MECHANISM IN THE THERMAL STABILIZATION OF POLY(VINYL CHLORIDE) .2. ACTION OF METAL CHLORIDES

By polaron theory, it is shown that the mechanism of dehydrochlorinati on (DHC) of PVC is determined by the interaction between the conjugate d double bonds in the polymer and the metal or organometallic chloride s. Lewis acid compounds, such as metal chloride, oxidize the pi electr ons of conjugated polyene sequences (CjPS) into polarons, which leads to accelerated chain DHC, By contrast, organotinchlorides can signific antly delay DHC, The difference can be explained by the effect of the alkyl chains in the organotin compounds. It has been demonstrated that , by controlling the cis configuration of CjPS existing initially or d eveloping in the polymer during the heat treatment, and by lowering th e Lewis acidity of the organotin chlorides, the alkyl chains attached to the central metal atom contribute their stabilization effect by inh ibiting the proliferation of polarons or by favoring the readdition re action of HCl to conjugated double bonds and the cyclization of the po lymer chain.